ANALOGICTECH AAT1271IWO-T1

PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
General Description
Features
The AAT1271 is a high-efficiency, high-current boost
converter capable of 1.5A typical output current. It is an
ideal power solution for LED photo flash applications in
all single cell Li-ion powered products.
• VIN Range: 2.7V to 5.5V
• Dual Channel Output
• Up to 1.5A Regulated Output Current (750mA per
channel)
• Up to 85% Efficiency with Small Inductor (1μH)
• 2 MHz Switching Frequency
• Separate Flash Enable
• Separate Flash Inhibit
• User-Programmable Safety Timer
• Single Resistor Sets Flash and Movie Mode Current
• AS2Cwire Single Wire Programming:
▪ Movie Mode Current
▪ Flash/Movie Mode Current Ratio
▪ Movie Mode Output Configuration
▪ Flash Safety Timer
• True Load Disconnect
• Input Current Limit
• Over-Voltage (Open LED, Open Circuit), Short Circuit,
and Over-Temperature Protection
• Shutdown Current < 1.0μA
• 14-pin TDFN 3x3 mm Package
• -40°C to +85°C Temperature Range
The AAT1271 maintains output current regulation by
switching the internal high-side and low-side switch
transistors. The transistor switches are pulse-width
modulated at a fixed frequency of 2MHz. The high
switching frequency allows the use of a small inductor
and output capacitor, making the AAT1271 ideally suited
for small battery-powered applications.
AnalogicTech’s proprietary AS2Cwire™ (Advanced Simple
Serial Control™) serial digital interface is used to enable,
disable, configure, and program the operation of the
AAT1271. Using the AS2Cwire interface, the movie-mode
current level for each LED, the safety timer delay, and the
flash-to-movie-mode current ratio can be programmed to
one of 16 levels. In addition, the single-wire serial protocol sets output channel control. The AAT1271 also
includes a separate Flash Enable input to initiate both the
flash operation and the default timer which can be used
either to terminate a flash event at the end of a userprogrammed delay or as a safety feature. Also included
is a Flash Inhibit pin which reduces the flash current to
movie-mode levels during high battery demand.
The maximum flash and movie-mode current is set by one
external resistor where the ratio of Flash to Movie-mode
current is set at approximately 7.3:1. One or two LEDs can
be connected to the AAT1271, where in the case of two
LEDs the output current is matched between each diode.
Applications
•
•
•
•
•
Camcorder Video Light (Torch Light)
Cellphones/Smartphones
Digital Still Cameras (DSCs)
LED Photo Flash/Torch
Mobile Handsets
The AAT1271 contains a thermal management system to
protect the device in the event of an output short-circuit
condition. Built-in circuitry prevents excessive inrush
current during start-up. The shutdown feature reduces
quiescent current to less than 1.0μA.
The AAT1271 is available in a Pb-free, thermally-enhanced
14-pin 3x3mm TDFN package.
1271.2008.08.1.1
www.analogictech.com
1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Typical Application
L1
1μH
High Current
Flash LEDs
SW
IN
OUT
CIN
2.2μF
VBAT
AAT1271
Movie-mode
Enable and Set
Flash Enable
Flash Inhibit
COUT
2.2μF
EN/SET
FLOUTA
FLEN
FLOUTB
FLINH
CT
RSET
GND AGND PGND FLGND
CT
RSET
107kΩ
Pin Descriptions
Pin #
Symbol
1
CT
2
EN/SET
3
FLEN
4
AGND
5
IN
6
SW
7
PGND
8
OUT
9
GND
10
FLINH
11
FLOUTB
12
FLGND
13
FLOUTA
14
RSET
EP
2
Function
Flash timer control input. Connect a capacitor between CT and AGND to set maximum duration of the flash
pulse. To disable the flash timer, connect CT to AGND.
Enable and Serial Control input. EN/SET is the AS2Cwire addressing and programming input to: a) adjust
the movie-mode current level; b) program the flash timer based on CT; c) select the Flash-to-Movie-mode
ratio; and d) select FLOUTA and FLOUTB’s output configuration.
Flash enable pin. A low-to-high transition on the FLEN pin initiates a flash pulse and starts the flash timer.
Analog ground pin. Connect AGND to PGND, GND, and FLGND at a single point as close to the AAT1271 as
possible.
Power input. Connect IN to the input power supply voltage. Connect a 2.2μF or larger ceramic capacitor
from IN to PGND as close as possible to the AAT1271
Boost converter switching node. Connect a 1μH inductor between SW and IN.
Power ground pin. Connect PGND to AGND, GND, and FLGND at a single point as close to the AAT1271 as
possible.
Power output of the boost converter. Connect a 2.2μF or larger ceramic capacitor from OUT to PGND as
close as possible to the AAT1271. Connect OUT to the anode(s) of the Flash LED(s).
Ground pin. Connect GND to PGND, AGND, and FLGND at a single point as close to the AAT1271 as possible.
Flash inhibit pin. FLINH is an active HIGH control input with an internal 200kΩ resistor to AGND. A low-tohigh transition on the FLINH pin reduces FLOUTA and FLOUTB output currents to the maximum (default)
movie-mode current level for the duration of FLINH. Strobing the FLINH pin low to high does not reset the
flash timer.
Flash Output B. Connect cathode of Flash LEDB to FLOUTB. For a single flash LED, connect FLOUTB &
FLOUTA together. For two flash LEDs, each output will conduct 50% of the total flash output current.
Flash ground pin. Connect FLGND to PGND, GND, and AGND at a single point as close to the AAT1271 as
possible
Flash Output A. Connect cathode of Flash LEDA to FLOUTA. For a single flash LED, connect FLOUTA and
FLOUTB together. For two flash LEDs, each output will conduct 50% of the total flash output current.
Flash current setting input. A 107kΩ resistor from RSET to AGND sets the maximum flash current available at FLOUTA and FLOUTB to 1.5A. Each FLOUTA and FLOUTB channel will conduct 50% of the maximum
programmed current. The AAT1271’s flash-to-movie-mode ratio is fixed at 7.3:1.
Exposed paddle (bottom); Connect EP to PGND as close as possible to the AAT1271.
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Pin Configuration
TDFN33-14
(Top View)
CT
EN/SET
FLEN
AGND
IN
SW
PGND
1
14
2
13
3
4
12
EP
11
5
10
6
9
7
8
RSET
FLOUTA
FLGND
FLOUTB
FLINH
GND
OUT
Absolute Maximum Ratings1
(TA = 25°C unless otherwise noted.)
Symbol
IN, SW, OUT
RSET, EN/SET, FLEN, FLINH, CT,
FLOUTA, FLOUTB
TJ
Ts
TLEAD
Description
Value
Units
Maximum Rating
-0.3 to 6.0
V
Maximum Rating
VIN + 0.3
V
-40 to 150
-65 to 150
300
°C
°C
°C
Value
Units
50
2
°C/W
W
Operating Temperature Range
Storage Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Recommended Operating Conditions
Symbol
θJA
PD
Description
Thermal Resistance
Maximum Power Dissipation
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. The AAT1271 is guaranteed to meet performance specifications over the -40°C
to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
1271.2008.08.1.1
www.analogictech.com
3
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Electrical Characteristics1
VIN = 3.6V; CIN = 2.2μF; COUT = 2.2μF; L = 1μH; RSET = 107kΩ; TA = -40°C to 85°C, unless otherwise noted. Typical
values are TA = 25°C.
Symbol
Description
Conditions
Power Supply
Input Voltage Range
VIN
VOUT(MAX)
Maximum Output Voltage
IIN(Q)
Min
Typ
2.7
Supply Current
ISHDN(MAX)
IFL(TOTAL)
IFL(MATCH)
VIN Shutdown Current
Total Output Current, Flash Mode
FLOUTA and FLOUTB Current Matching
IMM(LOAD)
Total Output Current, Movie Mode
fOSC
Switching Frequency
tDEFAULT
Default ON Time
Thermal Shutdown Threshold
TSD
TSD(HYS)
Thermal Shutdown Hysteresis
EN/SET/ FLEN/ FLINH Logic Control
VEN/SET(L),
EN/SET, FLEN Input Low Threshold
VFLEN(L)
VEN/SET(H),
EN/SET, FLEN Input High Threshold
VFLEN(H)
IEN/SET, IFLEN
EN/SET or FLEN Input Leakage Current
FLINH Input Threshold Voltage
VT(FLINH)
RIN(FLINH)
FLINH Input Resistance to AGND
tEN/SET(LOW)
EN/SET Serial Interface Low Time
tEN/SET(HI_ MIN)
Minimum EN/SET high Time
tEN/SET(HI_ MAX)
Maximum EN/SET High Time
tEN/SET(OFF)
EN/SET Off Timeout
tEN/SET(LAT)
EN/SET Latch Timeout
tFLEN_ON
FLEN ON Delay Time
tFLEN_OFF
FLEN OFF Delay Time
tFLINH_ON
FLINH ON Delay Time
tFLINH_OFF
FLINH OFF Delay Time
EN/SET = FLEN = IN, Set FL Load = 1.5A
EN/SET = IN, FLEN = AGND
EN/SET = FLEN = FLINH = GND
RSET = 107kΩ; FLOUTA + FLOUTB
RSET = 107kΩ , Movie Mode Current Set =
100%; FLOUTA + FLOUTB
TA = 25˚C
CT = 74nF
0.67
0.23
Max
Units
5.5
5.5
1
V
V
1
1.2
1.5
1.5
10
μA
A
%
206
mA
2.0
600
140
15
2.5
MHz
ms
°C
°C
0.4
V
1.4
FLEN/VEN/SET = VIN = 5V
V
-1
1
½VIN
200
0.3
75
50
75
500
500
EN/SET = GND
EN/SET = GND
mA
40
10
93
5
μA
V
kΩ
μs
ns
μs
μs
μs
μs
μs
μs
μs
1. The AAT1271 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
4
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
Efficiency vs. Input Voltage
Boost Switching Frequency vs. Input Voltage
(Movie and Flash Mode)
(Movie Mode; L = 1µH)
750mA/ch
102mA/ch
52mA/ch
26mA/ch
85
80
Efficiency (%)
Switching Frequency (MHz)
90
75
70
65
60
55
50
45
40
2.7
3.1
3.5
3.9
4.3
4.7
5.1
3
2.5
2
1.5
1
85°C
25°C
-40°C
0.5
0
5.5
2.7
3.1
3.5
4.7
5.1
Shutdown Current vs. Input Voltage
Supply Current vs. Input Voltage
5.5
(VEN = VFLEN = 3.6V)
1000
0.03
900
0.025
0.02
0.015
0.01
0.005
25°C
-40°C
0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
Supply Current (µA)
Shutdown Current (µA)
4.3
Input Voltage (V)
(VEN/SET = VFLEN = 0V)
800
700
600
500
400
300
85°C
25°C
-40°C
200
100
0
5.5
2.7
3.1
3.5
Input Voltage (V)
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Movie Mode Current Matching vs. Temperature
Movie Mode LED Current Accuracy vs. Input Voltage
(IFLOUTX = 103mA/Ch; VIN = 3.6V; L = 1µH)
(IFLOUTX = 103mA/Channel; L = 1µH)
120
10
115
8
Output Current (mA)
Output Current (mA)
3.9
Input Voltage (V)
110
105
100
95
90
FLOUTA
FLOUTB
85
80
6
4
2
0
-2
-4
-6
FLOUTA
FLOUTB
-8
-10
-40
-15
10
35
60
85
Temperature (°C)
1271.2008.08.1.1
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
www.analogictech.com
5
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
Movie Mode Output Ripple
Flash Mode Output Ripple
(IFLOUTX = 103mA/ch; VIN = 3.6V; L = 1µH)
(IFLOUTX = 750mA/ch; VIN = 4V; L = 1µH)
VOUT
(AC Coupled)
(50mV/div)
VOUT
(AC Coupled)
(50mV/div)
VINDUCTOR
(2V/div)
VINDUCTOR
(2V/div)
0V
IINDUCTOR
(100mA/div)
0V
IINDUCTOR
(50mA/div)
100mA
1.65A
Time (500ns/div)
Time (200ns/div)
Flash LED Current Matching vs. Temperature
Flash On Time Delay vs. Input Voltage
(IFLOUTX = 750mA/Ch; VIN = 4.2V; L = 1µH)
(IFLOUTX = 750mA/ch; COUT = 2.2µF; L = 1µH)
80
800
70
780
TFLEN_OND (µs)
Output Current (mA)
790
770
760
750
740
730
720
FLOUTA
FLOUTB
710
60
50
40
30
20
-40°C
25°C
85°C
10
0
700
-40
-15
10
35
60
85
2.7
Temperature (°C)
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Flash Timeout Delay vs. CT Capacitor
Movie Mode Line Transient
(IFLOUTX = 750mA/ch; VIN = 3.6V)
(IFLOUTX = 103mA/ch; VIN = 4.2V to 3.6V)
Flash Timeout (ms)
1200
1000
VIN
(500mV/div)
800
600
IFLOUTx
(AC Coupled)
(50mA/div)
400
200
0
0
20
40
60
80
100
120
140
CT Capacitor (nF)
6
4.2V
3.6V
Time (50µs/div)
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
VFLEN
(5V/div)
VOUT
(2V/div)
Flash Turn On Characteristic
Movie Mode to Flash Turn On Characteristic
(IFLOUTX = 750mA/ch; VIN = 3.6V; L = 1µH)
(IFLOUTX = 103mA to 750mA/ch; VIN = 3.6V; L = 1µH)
0V
VFLEN
(2V/div)
VOUT
(2V/div)
0V
VSINK
(2V/div)
0V
VSINK
(500mV/div)
IFLOUTX
(1A/div)
0V
IFLOUTX
(1A/div)
0V
2V
0V
0A
Time (50µs/div)
VEN/SET
(5V/div)
VOUT
(2V/div)
Time (50µs/div)
Movie Mode Turn On Characteristic
Movie Mode Transition Characteristic
(IFLOUTX = 103mA/ch; VIN = 3.6V; L = 1µH)
(IFLOUTX = 103mA to 188mA/ch; COUT = 0.22µF;
VIN = 3.6V; L = 1µH)
0V
VEN/SET
(2V/div)
VOUT
(2V/div)
0V
0V
VSINK
(500mV/div)
IFLOUTX
(100mA/div)
0V
VSINK
(500mV/div)
0V
IFLOUTX
(100mA/div)
0V
0A
0A
Time (100µs/div)
Time (100µs/div)
Flash Timeout vs. Temperature
EN, FLEN High Threshold Voltage
vs. Input Voltage
(IFLOUTX = 750mA/ch; VIN = 3.6V; CT = 47nF)
1.4
500
VEN/SET(H), VFLEN(H) (V)
Flash Timeout (ms)
1.3
450
400
350
300
250
1.2
1.1
1.0
0.9
0.8
0.7
85°C
25°C
-40°C
0.6
0.5
0.4
200
-40
-15
10
35
60
85
Temperature (°C)
1271.2008.08.1.1
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
www.analogictech.com
7
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Typical Characteristics
EN, FLEN Low Threshold Voltage
vs. Input Voltage
EN/SET Off Timeout vs. Input Voltage
1.4
300
VEN/SET(L), VFLEN(L) (V)
1.2
1.1
1.0
0.9
0.8
0.7
0.6
250
TEN/SET(OFF) (µs)
85°C
25°C
-40°C
1.3
200
150
85°C
25°C
-40°C
100
0.5
0.4
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
50
2.7
Input Voltage (V)
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
EN/SET Latch Timeout vs. Input Voltage
300
85°C
25°C
-40°C
TEN/SET(LAT) (µs)
250
200
150
100
50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
8
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Functional Block Diagram
IN
SW
OUT
FLOUTA
FLOUTB
EN/SET
Control
FLEN
FLINH
200kΩ
RSET
CT
Functional Description
The AAT1271 is a boost converter with a current regulated output designed to drive high current white LEDs
used in camera flash applications. The AAT1271 has two
channels to accurately regulate the current flow through
two separate white LEDs. There are two basic modes of
operation in the AAT1271; a Flash mode controlled by
the FLEN pin and the movie mode controlled through the
AS2Cwire interface.
Flash Mode
A flash pulse is initiated by strobing the FLEN input pin
low-to-high, which initiates a flash pulse and also starts
the internal timer. The maximum flash current in the
AAT1271 is set by an external resistor, RSET, which sets
the flash current and the maximum movie-mode current
reduced by a factor of 2. The flash timer will terminate
the flash current regardless of the status of the FLEN pin.
This can be either used as a simple flash timing pulse or
can be used as a safety timer in the event of a control
logic malfunction to prevent the LED from over-heating.
The maximum flash time is determined by an external
timing capacitor connected to the CT pin. The flash duration can be set from 50ms up to a maximum of 1s. The
AS2Cwire interface allows further adjustment of the flash
timer duration. This allows the flash timer duration to be
reduced in 16 linear steps from the maximum time set
by the timing capacitor. If the safety timer is not needed
in the application, it can be disabled by connecting the
CT pin directly to AGND.
1271.2008.08.1.1
AGND PGND FLGND GND
The AAT1271 has two LED current sources which share
the output current equally. For a single white LED application, the two current sources can be connected together to apply full output current into the LED. In two LED
applications, each diode can be connected to its corresponding current source (FLOUTA or FLOUTB) and the
output current will be shared. In applications where only
one LED is connected to either FLOUTA or FLOUTB, the
unused current sink must be directly connected to OUT,
thereby disabling that channel.
In mobile GSM systems where the phone remains in
constant contact with the base station by regular communication, a FLINH pin is provided to prevent both the
camera flash and PA transmission pulses from occurring
simultaneously. This avoids potential dips to the Li-ion
battery voltage below the system’s undervoltage lockout
threshold (UVLO). During a flash event, strobing the
FLINH pin low-to-high reduces the LED current to the
default movie-mode current level for the duration of
FLINH. Strobing FLINH high-to-low instructs the AAT1271
to revert the flash LED current to its maximum level,
assuming that the FLEN pin is still active (HIGH) and the
flash timer has not expired.
Movie Mode
The movie mode current level, channel enable, and the
flash to maximum movie mode current ratio are set
using the AAT1271’s AS2Cwire interface at the EN/SET
pin. The movie-mode current level can be adjusted in 16
steps using a logarithmic scale where each code is 1dB
below the previous code. Channel current outputs
(FLOUTA and FLOUTB) in movie-mode can be enabled or
www.analogictech.com
9
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
disabled individually or together. Lastly, the flash to
maximum movie mode current ratio can be set from 1:2
to 1:30 with respect to the maximum programmed flash
current. The FLEN signal takes priority over movie-mode
operation.
voltage automatically recovers when the over-temperature fault condition is removed.
Movie mode operation is controlled entirely by the
AS2Cwire interface via the EN/SET pin. Address 2 controls the movie mode on and off functions. Using this
register either or both of the LED channels can be turned
on to the current values set in Address registers 0 and
3. The movie mode is not operational when the FLEN pin
is high and the part is in flash mode operation. If the
AAT1271 is in movie mode (FLEN=low) and the FLEN is
strobed high the movie mode state will end and the part
will operate in the flash mode. The part will not reenter
movie mode when ENFL is brought low. To reenter movie
mode after a flash event the part must be turned off and
the AS2Cwire interface must be reprogrammed to the
desired movie mode level.
The AAT1271’s output voltage is limited by internal overvoltage protection circuitry, which prevents damage to
the AAT1271 from open LED or open circuit conditions.
During an open circuit, the output voltage rises and
reaches 5.5V (typical), and the OVP circuit disables the
switching, preventing the output voltage from rising
higher. Once the open circuit condition is removed,
switching will resume. The controller will return to normal operation and maintain an average output voltage.
Over-Voltage Protection
(Open LED, Open Circuit)
Auto-Disable Feature
The AAT1271 is equipped with an auto-disable feature
for each LED channel. After the IC is enabled and started
up, a test current of 2-3mA (typical) is forced through
each sink channel. The channel will be disabled if the
voltage of that particular SINK pin does not drop to a
certain threshold. This feature is very convenient for
disabling an unused channel or during an LED fail-short
event. This small test current should be added to the set
output current in both Flash and MM conditions.
Over-Temperature Protection
Thermal protection disables the AAT1271 when internal
power dissipation becomes excessive, as it disables both
MOSFETs. The junction over-temperature threshold is
140°C with 15°C of temperature hysteresis. The output
Timing Diagram
FLASH
FLASH
FLASH
FLASH
FLASH
FLASH TIMES OUT
tDLY(CT)
MOVIE MODE
NO FLASH
LED CURRENT
t DLY(CT)
NO FLASH
FLASH TIMES OUT
SET BY CT
FLASH LOWERED
TO DEFAULT
MOVIE-MODE
DURING FLINH
DATA TO
MOVIE-MODE
LEVEL
EN/SET
FLASH ENABLE
FLASH INHIBIT
No AS2C address programming shown.
10
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Applications Information
AS2Cwire Control of Movie Mode
Operation and Flash Safety Timer
LED Selection
In the AAT1271 control of the movie mode operation and
flash timer is managed by the Advanced Simple Serial
Control (AS2Cwire) interface. AS2Cwire relies on the
number of rising edges of the EN/SET pin to address and
load the AAT1271’s registers. As shown in Table 1,
Address 0 controls the Movie Current level as a percentage of the maximum movie mode current level. Address
1 controls the safety timer duration as a percentage of
the maximum value set by an external timing capacitor.
Address 2 enables the two LED channels independently
during movie mode. Finally, Address 3 sets the maximum possible current for movie mode operation. The
maximum movie mode current is set as a fraction of the
flash current with peak value of 1/2 and default value of
1/7.3. The last column in Table 1 shows the default values for each of the address registers.
The AAT1271 is specifically designed to drive white flash
LEDs (typical forward voltage of 2.5V to 4.0V). Since the
FLOUTA and FLOUTB input current sinks are matched
with low voltage dependence; the LED-to-LED brightness will be matched regardless of the individual LED
forward voltage (VF) levels.
Flash Mode LED Current
FLOUTA and FLOUTB can be programmed up to a maximum total flash current of 1.5A or up to 750mA per
channel. The output currents in FLOUTA and FLOUTB are
equal.
The maximum flash current in each FLOUTA and FLOUTB
is set by the RSET resistor. For the desired flash current in
each output, the resistor value can be calculated using
the following equation:
81kΩ × A 81kΩ × A
=
= 750mA per channel
IFLOUTA = IFLOUTB =
RSET
107kΩ
A flash event is initiated by asserting the FLEN pin. A
flash event is automatically terminated when FLEN is deasserted or if the safety timer terminates before the
FLEN pin is de-asserted. Any time that the FLINH pin is
asserted, the default movie-mode current level will
appear at both FLOUTA and FLOUTB. The default moviemode current level will be maintained on FLOUTA and
FLOUTB as long as the FLINH and FLEN pins are asserted, and the safety timer continues to run.
In addition to setting the flash current via RSET, the flash
current can be changed after FLEN is asserted by programming the movie mode current register with 16 different steps.
AS2Cwire Serial Interface
AS2Cwire latches data or address after the EN/SET pin
has been held high for longer than tLAT (500μs). Address
or data is differentiated by the number of EN/SET rising
edges. Since the data registers are 4 bits each, the differentiating number of pulses is 24 or 16, so that Address
0 is signified by 17 rising edges, Address 1 by 18 rising
edges and Address 2 by 19 rising edges and Address 3
by 20 rising edges. Data is applied to any number of rising edges between 1 and 16, inclusive. A typical write
protocol is a burst of EN/SET rising edges, signifying a
particular address, followed by a pause with EN/SET
held high for the prescribed tLAT timeout period, a burst
of rising edges signifying data, and a tLAT timeout for the
data registers. Once an address is set, then multiple
writes to the corresponding data register are allowed.
Address 0 is the default address on the first rising edge
after the AAT1271 has been disabled.
Address
EN/SET
Rising Edges
Function
Default
(No programming)
0
1
2
3
17
18
19
20
Movie Mode Current
Flash Safety Timer
Movie Mode Output Configuration
Flash/Movie Mode Current Ratio
100%
16/16
FLOUTA and FLOUTB OFF
1/7.3
Table 1: AS2Cwire Serial Interface Addressing.
1271.2008.08.1.1
www.analogictech.com
11
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
When EN/SET is strobed low and held low longer than
tOFF (500μs), the AAT1271 enters shutdown mode and
draws less than 1uA from VIN. All data and address are
cleared (reset to 0) during shutdown.
The AS2Cwire addressing allows the control of the moviemode output current, the safety timer delay, independent control of the FLOUTA and FLOUTB current sinks,
and the ratio of movie-mode current to flash current.
If there are no programmed write instructions applied to
the EN/SET pin prior to the assertion of the FLEN pin and
the device is enabled, then all registers will be loaded
with their default values shown in Table 1. In the event
that the number of rising edges applied at the EN/SET
pin is less than 17, the AAT1271’s state machine will
interpret instruction to program the output currents to
the desired current level for movie-mode operation.
movie mode operation, the maximum current available
at either FLOUTA or FLOUTB is then:
IMOVIE MODE[A/B] =
IFLOUT[A/B]MAX 750mA
=
= 103mA
7.3
7.3
Address 0 controls precise movie mode current levels.
The FLOUTA/FLOUTB movie-mode current can be adjusted in logarithmic fashion to one of 16 steps represented
as a fraction of the maximum movie mode current in
Table 2. To adjust the movie-mode current the user must
first access Address 0 before writing the data to set the
MM Current value.
Data
Percentage of Maximum MM Current
1*
100%
2
89%
3
79%
4
71%
5
63%
6
56%
7
50%
8
45%
9
40%
10
36%
11
32%
12
28%
13
25%
14
22%
15
20%
16
0%
Movie Mode Current – Address 0
The AAT1271 movie mode current settings are controlled
using the AS2Cwire interface. Movie Mode current has a
maximum value of 50% of the flash current with 240
possible current levels. The maximum movie mode current is set by Address register 3 (discussed below). The
default ratio between the flash current level and maximum movie mode current level is 1:7.3. The corresponding FLOUTA/FLOUTB maximum movie mode current can be calculated:
I
IMOVIE MODE[A/B] = FLOUT[A/B]MAX
7.3
For example, if an RSET value of 107kΩ is chosen, then
the FLOUTA/FLOUTB flash current is set to 750mA. For
Table 2: Address 0, Movie Mode
Current Programming.
Address
Data
T HI
T LO
TLAT
TLAT
EN/SET
1
Address
Data Reg 1
2
16
17
1
0
2...
n ≤ 16
1
0
n
Figure 1: AS2CwireTM Serial Interface Timing.
* Denotes the default value.
12
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Flash/Safety Timer – Address 1
A timer function that enables the flash current sinks for
a programmed amount of time is incorporated in the
AAT1271. The on-time is programmed by loading the
Timing Register at Address 1 with a value from 1 to 16
and by choosing a value for the external timing capacitor, CT (see Table 3). When data is latched into Address
1, the data will be used at the next occurrence of an
asserted FLEN, it will then revert back to the default
value of Data 1, or 16/16. This feature eliminates the
need for an external, housekeeping baseband controller
to contain a safety delay routine. It also serves as a
protection feature to minimize thermal issues with the
Flash LEDs in the event an external controller’s flash
software routine experience hang-up or freeze. If no
write instruction is applied to Address 1, then the safety
timer will default to the maximum delay programmed
externally at CT.
The Flash Time T can be calculated by the following
equation:
T = 7.98s/μF · CT (μF)
Data
Ratio of MM Timeout
1*
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
16/16
15/16
14/16
13/16
12/16
11/16
10/16
9/16
8/16
7/16
6/16
5/16
4/16
3/16
2/16
1/16
Table 3: Address 1, Flash Safety Timer
Programming; Maximum Value
Programmed by CT.
Output Enable Control – Address 2
Where T is in seconds and CT is in μF.
For example, using a 47nF capacitor at CT sets the flash
timeout to:
Flash Timeout = 7.98s/μF · 47nF = 375ms
The relationship between the flash safety timeout and
the capacitance of the timer capacitor is illustrated in
Figure 2.
In the case where two LEDs are used, each output can
be enabled or disabled independently in movie mode as
shown in Table 4. To enable or disable either or both
FLOUTA and FLOUTB, a write instruction to Address 2 is
applied to the AAT1271’s EN/SET pin. If no write instruction is applied, the default value for Address 2 is FLOUTA,
FLOUTB = OFF. During a flash event, both FLOUTA and
FLOUTB will be enabled regardless of the movie-mode
setting.
Flash Timeout (ms)
1200
Selection
1000
800
600
400
Data
FLOUTA
FLOUTB
1*
2
3
4
OFF
OFF**
ON
ON
OFF
ON
OFF**
ON
Table 4: Address 2, Movie Mode
Output Configuration.
200
0
0
20
40
60
80
100
120
140
CT Capacitor (nF)
Figure 2: Flash Safety Timeout
vs. Timer Capacitor.
* Denotes the default value.
** A small current will flow due to the start-up test current.
1271.2008.08.1.1
www.analogictech.com
13
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Flash to Maximum Movie Mode
Current Ratio – Address 3
Shutdown
The maximum movie-mode current is a fixed ratio of the
flash current controlled by Address 3. The ratio may be
varied from 1:2 to OFF in 16 linear steps as shown in
Table 5. The default value for Address 3 is Data=4 and
represents a flash to maximum movie mode current
level of 1 to 7.3.
Data
FL to MM Ratio
1
2
3
4*
5
6
7
8
9
10
11
12
13
14
15
16
1/2
1/3.8
1/5.5
1/7.3
1/8.9
1/10.5
1/12.2
1/13.8
1/14.9
1/16.5
1/18
1/19.6
1/21.1
1/22.6
1/24
OFF
Selecting the Boost Inductor
The AAT1271 controller utilizes PWM control and the
switching frequency is fixed. To maintain 2MHz maximum
switching frequency and stable operation, a 1μH inductor
is recommended. Manufacturer’s specifications list both
the inductor DC current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the saturation characteristics. Measurements at
full load and high ambient temperature should be performed to ensure that the inductor does not saturate or
exhibit excessive temperature rise.
Table 5: Address 3, Flash/Movie
Mode Current Ratio.
The default maximum movie mode current can be calculated:
IMOVIE MODE[A/B] =
IFLOUT[A/B]MAX
7.3
For example, if an RSET value of 107kΩ is chosen, then
the FLOUTA/FLOUTB flash current is set to 750mA. For
movie mode operation, the maximum current available
at either FLOUTA or FLOUTB is then:
IMOVIE MODE[A/B] =
IFLOUT[A/B]MAX 750mA
=
= 103mA
7.3
7.3
The maximum movie mode current level can be calculated using the following equation:
IMOVIEMODE[A/B] =
Since the sink switches are the only power returns for all
loads, there is no leakage current to load if all the sink
switches are disabled. When EN/SET pin is held low for
an amount of time greater than tOFF (500μs), the
AAT1271 enters shutdown mode and draws less than
1μA from VIN. All data and address registers are cleared
(reset to 0) during shutdown.
The inductor (L) is selected to avoid saturation at minimum input voltage and maximum output load conditions.
Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Bench
measurements are recommended to confirm actual IPEAK
and to ensure that the inductor does not saturate at
maximum LED current and minimum input supply voltage. The RMS current flowing through the boost inductor
is equal to the DC plus AC ripple components. Under
worst case RMS conditions, the current waveform is
critically continuous. The resulting RMS calculation yields
worst case inductor loss. The RMS current value should
be compared against the inductor manufacturer’s temperature rise, or thermal derating guidelines:
IRMS =
IPEAK
3
For a given inductor type, smaller inductor size leads to
an increase in DCR winding resistance and, in most
cases, increased thermal impedance. Winding resistance
degrades boost converter efficiency and increases the
inductor’s operating temperature:
81kΩ × A
1
=
= Max Movie Mode Current
RSET
FL to MM Ratio
PLOSS(INDUCTOR) = I2RMS · DCR
*Denotes the default value.
14
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Selecting the Boost Capacitors
In general, it is good design practice to place a decoupling capacitor (input capacitor) between the IN and GND
pins. An input capacitor in the range of 2.2μF to 10μF is
recommended. A larger input capacitor in this application
may be required for stability, transient response, and/or
ripple performance. The high output ripple inherent in
the boost converter necessitates the use of low impedance output filtering. Multi-layer ceramic (MLC) capacitors provide small size and adequate capacitance, low
parasitic equivalent series resistance (ESR) and equivalent series inductance (ESL), and are well suited for use
with the AAT1271 boost regulator. MLC capacitors of type
X7R or X5R are recommended to ensure good capacitance stability over the full operating temperature range.
The output capacitor is selected to maintain the output
load without significant voltage droop (∆VOUT) during the
power switch ON interval. A 2.2μF ceramic output capacitor is recommended (see Table 7). Typically, 6.3V or 10V
rated capacitors are required for this flash LED boost
output. Ceramic capacitors selected as small as 0603 are
available which meet these requirements. MLC capacitors
exhibit significant capacitance reduction with applied
voltage. Output ripple measurements should confirm
that output voltage droop and operating stability are
within acceptable limits. Voltage derating can minimize
this factor, but results may vary with package size and
among specific manufacturers. To maintain stable operation at full load, the output capacitor should be selected
to maintain ∆VOUT between 100mV and 200mV. The boost
converter input current flows during both ON and OFF
switching intervals. The input ripple current is less than
the output ripple and, as a result, less input capacitance
is required.
PCB Layout Guidelines
Boost converter performance can be adversely affected
by poor layout. Possible impact includes high input and
output voltage ripple, poor EMI performance, and
reduced operating efficiency. Every attempt should be
made to optimize the layout in order to minimize parasitic PCB effects (stray resistance, capacitance, and
inductance) and EMI coupling from the high frequency
SW node. A suggested PCB layout for the AAT1271 1.5A
step-up regulator is shown in Figures 3 and 4. The following PCB layout guidelines should be considered:
1.
2.
3.
4.
5.
Minimize the distance from capacitor CIN and COUT’s
negative terminals to the PGND pins. This is especially true with output capacitor COUT, which conducts
high ripple current from the output to the PGND pins.
Minimize the distance under the inductor between IN
and switching pin SW; minimize the size of the PCB
area connected to the SW pin.
Maintain a ground plane and connect to the IC PGND
pin(s) as well as the PGND connections of CIN and
COUT.
Consider additional PCB exposed area for the flash
LEDs to maximize heatsinking capability. This may
be necessary when using high current application
and long flash duration application.
Connect the exposed paddle (bottom of the die) to
either PGND or GND. Connect AGND, FLGND to GND
as close as possible to the package.
Manufacturer
Part Number
Inductance
(μH)
Saturated Rated
Current (A)
DCR
(mΩ)
Size (mm)
LxWxH
Cooper Bussmann
Cooper Bussmann
Cooper Bussmann
Sumida
Coilcraft
SD3812-1R0-R
SDH3812-1R0-R
SD10-1R0-R
CDH38D11/S
LPS4012-102NLC
1
1
1
1
1
2.69
3
2.25
2.8
2.5
48
45
44.8
48.8
60
4.0x4.0x1.2
3.8x3.8x1.2
5.2x5.2x1.0
4.0x4.0x1.2
4.1x4.1x1.2
Type
Shielded
Shielded
Shielded
Shielded
Shielded
Drum
Drum
Drum
Drum
Drum
Core
Core
Core
Core
Core
Table 6: Typical Suggested Surface Mount Inductors.
Manufacturer
Murata
Part Number
Capacitance (μF)
Voltage Rating (V)
Temp Co.
Case Size
GRM185R60J225KE26
GRM188R71A225KE15
GRM21BR70J225KA01
GRM21BR71A225KA01
GRM219R61A475KE19
2.2
2.2
2.2
2.2
4.7
6.3
10
6.3
10
10
X5R
X7R
X7R
X7R
X5R
0603
0603
0805
0805
0805
GRM21BR71A106KE51
10
10
X7R
0805
Table 7: Typical Suggested Surface Mount Capacitors.
1271.2008.08.1.1
www.analogictech.com
15
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
DC-
DC+
JP6
MCU
R5
10K
R6
10K
R7
10K
1
2
3
4
SW1
Movie Mode Control
0
2
4
U2
1
3
5
SW2
Safety Timer
0
2
4
VDD
GP5
GP4
GP3
VSS
GP 0
GP 1
GP 2
PIC12F675C3
1
3
5
0
2
4
R10
0
10k
C4
1μF
FLINH
FLEN
R9
330
LED2
GRN
SW3
A/B Control
8
7
6
5
JP7
0
R8
330
LED 1
RED
0
2
4
SW4
2
4
1
3
5
JP3
SW5
JP4
D1
U1
R2
100K
JP5
EN /SET
L1
1μH
C1
2.2μF
C3
74 nF
1
2
3
4
5
6
7
VOUT
JP1
0
R4
100k
( opt)
R3
100k
1
3
5
1
3
5
CT
EN/SET
FLEN
AGND
IN
SW
PGND
RSET
FLA
FLGND
FLB
FLINH
GND
OUT
JP2
0
D2
14
13
12
11
10
9
8
AAT1271 TDFN33-14
R1
107k
L1
C1, C2
C3
D1, D2
C2
2.2μF
Cooper Bussmann SD3812-1R0-R, 1μH, 2.69A, 48mΩ
Murata GRM188R71A225KE15 2.2μF, 0603, X7R, 10V
Murata GRM155R71A743KA01, 74nF, 0402, X7R, 10V
Lumiled LXCL-PWF4 or equivalent
Figure 2: AAT1271 Evaluation Board Schematic.
Figure 3: AAT1271 Evaluation Board
Top Side Layout.
16
Figure 4: AAT1271 Evaluation Board
Bottom Side Layout.
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
Component
1.5A Step-Up Current Regulator for Flash LEDs
Part Number
U1
AAT1271IWO
U2
SW1 – SW3
R1
R2, R3, R4
R5, R8
R6, R7
JP1, JP2, JP7
C1, C2
C3
C4
L1
D1-D2
LED1
LED2
JP3, JP4, JP5, JP6
PIC12F675
PTS645TL50
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
GRM188R71A225KE15
GRM155R71A743KA01
GRM216R61A105KA01
SD3812-1R0-R
LXCL-PWF4
CMD15-21SRC/TR8
CMD15-21VGC/TR8
PRPN401PAEN
Description
1.5A Step-Up Current Regulator for Flash LEDs;
TDFN33-14 package
8-bit CMOS, FLASH-based μC; 8-pin PDIP package
Switch, SPST, 5mm
107kΩ, 1%, 1/4W; 0402
100kΩ, 1%, 1/4W; 0603
10kΩ, 5%, 1/4W; 0603
330Ω, 5%, 1/4W; 0603
0Ω, 5%
2.2μF, 10V, X7R, 0603
74nF, 10V, X7R, 0402
1μF, 10V, X5R, 0805
Drum Core, 1μH, 2.69A, 48mΩ
White Flash LED
Red LED; 1206
Green LED; 1206
Conn. Header, 2mm zip
Manufacturer
AnalogicTech
Microchip
ITT Industries
Vishay
Vishay
Vishay
Vishay
Vishay
Murata
Murata
Murata
Cooper Bussmann
Lumileds, Philips
Chicago Miniature Lamp
Chicago Miniature Lamp
Sullins Electronics
Table 8: AAT1271 Evaluation Board Bill of Materials.
1271.2008.08.1.1
www.analogictech.com
17
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TDFN33-14
ZUXYY
AAT1271IWO-T1
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means semiconductor
products that are in compliance with current RoHS standards, including the requirement that lead not exceed
0.1% by weight in homogeneous materials. For more information, please visit our website at
http://www.analogictech.com/about/quality.aspx.
Package Information
TDFN33-143
Detail "A"
3.000 ± 0.050
2.500 ± 0.050
Index Area
3.000 ± 0.050
1.650 ± 0.050
Top View
Bottom View
+ 0.100
- 0.000
Pin 1 Indicator
(Optional)
0.180 ± 0.050
Side View
0.400 BSC
0.000
0.203 REF
0.750 ± 0.050
0.425 ± 0.050
Detail "A"
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN, and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
18
www.analogictech.com
1271.2008.08.1.1
PRODUCT DATASHEET
AAT1271
SwitchRegTM
1.5A Step-Up Current Regulator for Flash LEDs
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual
property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and
conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate
design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to
support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other
brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
1271.2008.08.1.1
www.analogictech.com
19